The invention relates to an arrangement for effecting a very rigid connection between relatively thin sheet material and a heavier member. A typical example of such a structure in the connection between fan blade members and the like, with a central hub member, by means of which the blade member is adapted to be connected to a rotatable drive shaft or the like. Other examples of this type of structure are for bushings, sleeves, and various types of fasteners.
For the purpose of illustration, the invention will be described and explained in connection with the connection of relatively thin fan blade members with a relatively heavy hub member, where problems of torque transmittal are involved.
It is common practice in the construction of fan blades and the like, having a central hub member, to secure a tubular-shaped hub member to a flat sheet-like central hub receiving portion of the fan blade or other structure, by forming the hub member with an axially extending sleeve adapted to be inserted into a bore in such central hub receiving portion of the blade member, with the sleeve having an outer diameter approximately equal to the diameter of the central bore of the blade member. The hub member is provided with an outwardly extending shoulder at the inner end of the sleeve, upon which the adjacent face of the blade member abuts.
The sleeve of the hub member is designed with such a length that, following insertion in the bore of the blade member, it may be suitably formed, as for example by a swaging or spinning operation, or the like, into an outwardly extending flange which overlies the peripheral portions of the blade member defining the bore therein, thus clamping the blade member between the shoulder and flange of the hub member.
While such clamping action may, at least initially, firmly clamp the hub and blade members, often following use, the blade member may become relatively loose on the hub member and the frictional engagement between the two parts, which must carry all torque forces transmitted by the hub to the blade member, become reduced to a point where slippage may take place therebetween.
While it is possible to form the hub member with a central bore which includes one or more integral keys or splines, adapted to cooperate with corresponding splines initially on the hub member, the fabrication of the individual blade and hub members with key or spline configurations becomes relatively costly and thus increases the cost of the assembly.